Container, and thermal forming device and thermal forming method therefor

ABSTRACT

The present invention provides a bottomed cylindrical container, comprising a body wall, a bottom wall, and a ring-shaped foot downwardly extending from the bottom wall, said container being produced by thermo-molding a resin sheet, characterized in that said foot is formed by folding an inner wall by compressed fluid to be fusion-bonded with an outer wall, so as to form the foot comprising the inner wall and the outer wall. The present invention also provides a bottomed cylindrical container, comprising a body wall having a grounding edge at a lower end thereof, and a bottom wall, said container being produced by thermo-molding a resin sheet, characterized in that said bottom wall connects with an upper edge of an inner wall produced by folding back the body wall along the grounding edge and by fusion-bonding it to an inner periphery of the body wall. In addition, the present invention provides the methods for thermo-molding these containers and their apparatuses.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a container and a thermo-moldingapparatus and a thermo-molding method for molding such a container. Moreparticularly, the present invention relates to a legged and bottomedcylindrical thin wall container or a bottomed cylindrical containerhaving the bottom wall connected to the inner barrel of the body sectionproduced by folding the latter back at the grounding edge of thecontainer, which is molded by thermo-molding and made free from any gapin the inside of the junction of the leg or the body inner barrel andthe body wall, and also a thermo-molding apparatus and a thermo-moldingmethod for molding such a container.

[0002] Legged and bottomed containers molded by thermo-molding athermoplastic resin sheet and made free from any gap in the inside atthe site corresponding to the leg shaped by bending the sheet andthermo-molding apparatus and thermo-molding methods for molding suchbottomed containers are known to date. For example, Japanese PatentLaid-open Nos. 2000-225642 and 2001-001395 disclose such bottomedcontainers and thermo-molding apparatus and thermo-molding methods formolding such bottomed containers.

[0003] According to the above patent documents describing the prior art,a bottomed container is thermo-molded either by using a thermo-moldingapparatus comprising an upper plug unit having a pressure molding plugand cooling male mold, and a unit of female mold including an upper moldfor forming the mouth section and the body peripheral section of thecontainer, an intermediate mold for forming the lower part of the bodyperipheral section and the outer peripheral surface of the bottom rim(or foot) and a bottom mold for forming the inner peripheral surface ofthe bottom rim and the bottom wall or by using a thermo-moldingapparatus comprising a pressure molding plug, a female mold and a bottommold.

[0004] More specifically, a container is molded by pushing the pressuremolding plug into the female mold to shape the container so as to makeit show the profile of the surface of the female mold, while holding thebottom mold to the lowered position, and subsequently raising the bottommold to form the bottom wall and the bottom rim respectively on theupper surface of the bottom mold and between the bottom mold and thefemale mold.

[0005] The bottom rim is made either to flare toward the lower end andshow a triangular cross section or to show a cylindrical profile that isvertically extending with a same diameter.

[0006] With the prior art, regardless if the bottom rim is flared ormade to show a vertically extending cylindrical profile, the differencebetween the outer diameter of the upper end of the mold surface of thefemale mold (more particularly its intermediate mold) for forming theouter peripheral surface of the bottom rim and the outer diameter of themold surface of the bottom mold for forming the inner peripheral surfaceof the bottom rim is greater than the thickness of the resin sheet andslightly smaller than the twice of the thickness because the bottom rimis formed between the mold surface of the mold surface of the femalemold (more particularly its intermediate mold) and that of the bottommold.

[0007] Therefore, if twice of the resin sheet that is used for producingthe container is smaller than the difference of the diameters, a gap isproduced along the inner surface of the container at the site thatcorresponds to the bottom rim.

[0008] This means that, with either of the above describedthermo-molding apparatus and the corresponding molding method, it is notfeasible to use resin sheets having different thicknesses andparticularly thin resin sheets cannot be used.

[0009] If thin resin sheets are to be used, the difference between theouter diameter of the upper end of the mold surface of the female mold(more particularly its intermediate mold) for forming the outerperipheral surface of the bottom rim and the outer diameter of the moldsurface of the bottom mold for forming the inner peripheral surface ofthe bottom rim needs to be reduced.

[0010] Additionally, the thickness of resin sheet can show variances inthe stages before forming the bottom rim because the thickness of theoriginal roll, the thermo-molding temperature, the degree of vacuum andthe timing of applying compressed air can vary significantly. Therefore,it is very difficult to constantly maintain the molding conditions thatmake the thickness of the bent resin sheet slightly greater than the gapbetween the metal molds.

[0011] Thus, while the above described problem may be relativelyinsignificant when molding a large container by using a thick resinsheet, the thickness may have to be more rigorously controlled when arelatively thin resin sheet is used. In other words, the prior art isnot suited for molding small containers.

SUMMARY OF THE INVENTION

[0012] Therefore, it is the object of the present invention to dissolvethe above identified problem and provide a legged and bottomedcylindrical container having no gap in the inside of the foot or abottomed cylindrical container having no gap between the inner barrel ofthe body produced by bending the original resin sheet at the groundingedge and the body wall, a thermo-molding apparatus and a thermo-moldingmethod for molding such a container.

[0013] According to the invention, the above object is achieved byproviding a bottomed cylindrical container, comprising a body wall, abottom wall, and a ring-shaped foot downwardly extending from the bottomwall, said container being produced by thermo-molding a resin sheet;characterized in that said foot is formed by folding an inner wall bycompressed fluid to be fusion-bonded with an outer wall, so as to formthe foot comprising the inner wall and the outer wall. Preferably, saidbottom wall comprises a central section and a peripheral section, andthe peripheral portion is made thin.

[0014] According to another aspect of the invention, the above object isachieved by providing a bottomed cylindrical container, comprising abody wall having a grounding edge at a lower end thereof, and a bottomwall, said container being produced by thermo-molding a resin sheet,characterized in that said bottom wall connects with an upper edge of aninner wall produced by folding back the body wall along the groundingedge and by fusion-bonding it to an inner periphery of the body wall.

[0015] The present invention also provides an apparatus forthermo-molding a resin sheet to a bottomed cylindrical container,comprising an upper mold having a plug, and a lower mold having a femalemold and a bottom bush; wherein said female mold has mold surfaces forforming a body wall of the container; and said bottom bush hascompressed air blow-in holes. Also, it provides an apparatus forthermo-molding a resin sheet to a bottomed cylindrical container with aring-shaped foot, comprising an upper mold having a plug, and a lowermold having a female mold and a bottom bush, wherein; said female moldis provided with suction holes; said female mold has a mold surface forforming a body wall of the container, a mold surface for forming abottom peripheral wall of the container, and a mold surface for formingan outer wall of the foot; and said bottom bush has compressed fluidblow-in holes. Preferably, said lower mold comprises a mold base, thebottom bush in the mold base, and the female mold on the mold base; agap is formed between a lower surface of the female mold and the moldbase; and an annular suction groove is formed between a lower surface ofthe female mold and the mold base, and communicates with the gap.

[0016] Another aspect of the present invention provides a method forthermo-molding a footed and bottomed cylindrical container; comprisingheating a thermoplastic resin sheet; pressing the heated sheet by a plugof an upper mold with vacuum-sucking, to contact the sheet with moldsurfaces of a female mold of a lower mold, so as to form a body wall andan outer wall of a foot of the container; and blowing compressed fluidthrough blow-in holes of a bottom bush of the lower mold into the femalemold with vacuum-sucking, to contact the sheet on a top surface of thebottom bush with a bottom surface of the plug, so as to form a bottomwall and an inner wall of the foot, said inner wall being fusion-bondedwith the outer wall.

[0017] Still another aspect of the present invention provides a methodfor thermo-molding a bottomed cylindrical container; comprising heatinga thermoplastic resin sheet; pressing the heated sheet by a plug of anupper mold with vacuum-sucking, to contact the sheet with mold surfacesof a femal mold of a lower mold, so as to form a body wall of thecontainer; and blowing compressed fluid through blow-in holes of abottom bush of the lower mold into the female mold with vacuum-sucking,to contact the sheet on a top surface of the bottom bush with a bottomsurface of the plug, so as to form a bottom wall and an inner wall beingfusion-bonded with the body wall.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1A is a schematic front view of the first embodiment oflegged and bottomed container according to the invention, showing itpartly in cross section.

[0019]FIG. 1B is an enlarged partial view of the embodiment, showing aprincipal part thereof.

[0020]FIG. 2 is a schematic front view of the first embodiment ofthermo-molding apparatus according to the invention, showing it partlyin cross section.

[0021]FIG. 3 is a schematic front view of the first embodiment ofthermo-molding apparatus of FIG. 2, showing it partly in cross sectionand illustrating the state where the molds are closed and the plug ismade to start lowering.

[0022]FIG. 4A is a schematic front view of the first embodiment ofthermo-molding apparatus of FIG. 2, showing it partly in cross sectionand illustrating the state where the plug reaches the lowest positionand the vacuum molding operation is completed.

[0023]FIG. 4B is an enlarged partial view of the embodiment of FIG. 4A.

[0024]FIG. 5 is a schematic front view of the first embodiment ofthermo-molding apparatus of FIG. 2, showing it partly in cross sectionand illustrating the state the bottom of the container is molded byapplying compressed air.

[0025]FIG. 6 is a schematic front view of the first embodiment ofthermo-molding apparatus of FIG. 2, showing it partly in cross sectionand illustrating the state where the operation of molding the bottom ofthe container by applying compressed air is completed.

[0026]FIG. 7 is a schematic front view of the second embodiment oflegged and bottomed container according to the invention, showing itpartly in cross section.

[0027]FIG. 8 is a schematic front view of the second embodiment ofthermo-molding apparatus, showing it partly in cross section andillustrating the state where the plug reaches the lowest position andthe vacuum molding operation is completed.

[0028]FIG. 9 is a schematic front view of the second embodiment ofthermo-molding apparatus of FIG. 8, showing it partly in cross sectionand illustrating the state where the operation of molding the bottom ofthe container by applying compressed air is completed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Now, the present invention will be described in detail byreferring to the accompanying drawings that illustrate preferredembodiments of the invention.

[0030] Firstly, the first embodiment of footed and bottomed cylindricalcontainer or footed bowl-shaped container A will be described.

[0031] As shown in FIG. 1, a footed and bottomed cylindrical container Acomprises a body wall 2 having an outwardly directed flange 1 arrangedalong a peripheral edge of a top opening, a bottom wall 3, and aring-shaped foot 4 extending downwardly from the bottom wall 3.

[0032] The body wall 2 is curved inwardly at and near a lower endthereof until it becomes horizontal and reaches to the foot 4. Suchhorizontal part is a bottom peripheral wall 5 which connects to thebottom wall 3. The bottom wall 3 is located within the foot 4, andcomprises a central section 6 a and a thin peripheral section 6 b.

[0033] The foot 4 comprises an outer wall 7 a and an inner wall 7 bwhich is produced by inwardly folding back the outer wall 7 a along at alower edge thereof and welded to the outer wall. An outwardly bulge 8 isformed along a lower peripheral edge of the foot 4.

[0034] Preferable resin materials that can be used for forming thecontainer A include poly-olefin type resins such as polypropylene (PP)and polyethylene (PE), although other thermo-moldable synthetic resinmaterials or thermoplastic resin material such aspolyethyleneterephthalate (PET) can also suitably be used. The syntheticresin sheet to be used for molding may be of single layer or ofmultilayer (or laminate).

[0035] The synthetic resin sheet to be used for molding has a thicknessbetween 0.3 and 3.0 mm, while the wall thickness of the body wall of thecontainer obtained by thermo-molding the sheet is between about 0.1 andabout 0.45 mm.

[0036] Now, the first embodiment of thermo-molding apparatus B to beused for thermo-molding the first embodiment of container will bedescribed.

[0037] As shown in FIG. 2, the thermo-molding apparatus B comprises anupper mold C and a lower mold D.

[0038] The upper mold C comprises a cylindrical clamp 11 for pinchingthe sheet S, and a plug 10 vertically movable relative to the clamp 11.The sheet S is heated by a heater (not shown). The clamp 11 is notlimited to cylindrical shape.

[0039] The plug 10 has a cylindrical wall surface 12 and a flat bottomsurface 13. While the clamp 11 is so designed that compressed fluid(such as compressed air) is blown into it from above, it is notessential to blow compressed fluid into the clamp 11.

[0040] While the plug 10 of the illustrated embodiment shows acylindrical profile, it may alternatively show some other profile such aconical profile. Similarly, while the bottom surface 13 of plug of theillustrated embodiment is flat, it may alternatively be outwardly orinwardly curved depending on the molded product to be produced by usingit.

[0041] The lower mold D comprises a mold base 15, a female mold 16arranged on the mold base 15, and a bottom bush 17 arranged in an insideof the mold base 15.

[0042] The female mold 16 has a mold surface 18 for forming the bodywall 2 of the container A to be molded, a mold surface 19 for formingthe bottom peripheral wall 5, and a mold surface 20 for forming theouter peripheral surface of the foot 4. A passage 21 is arranged at thelower peripheral edge of the mold surface 20, so that a gap 21 isprovided between the lower surface of the female mold 16 and the moldbase 15. The gap 21 communicates with an annular suction groove 22.

[0043] The suction groove 22 communicates with a connection hole 23arranged in the mold base 15. The connection hole 23 communicates with avacuum unit (not shown). The female mold 16 is provided with acommunication hole 24. The communication hole 24 communicates with theconnection hole 23. A number of suction holes 25 are arranged near theupper edge and along the lower edge of the mold surface 18 of the femalemold 16, and each of the suction holes 25 communicates with thecommunication hole 24. Thus, air can be drawn from the inside of thefemale mold 16 through the connection hole 23, the suction groove 23,the gap 21 and the suction holes 25.

[0044] A number of blow-in holes 27 are formed at a center of the topsurface 26 of the bottom bush 17. A connection hole 28 is formed in thebottom bush 17, and communicates with a source of compressed fluid (notshown). Thus, compressed fluid is blown into the inside of the femalemold 16 through the communication hole 28 and the blow-in holes 27.

[0045] The bottom bush 17 is provided with a heater 29.

[0046] Now, the method of thermo-molding the container according to thefirst embodiment of the invention will be described below.

[0047] For the purpose of thermo-molding, the sheet S is heated by aheater (not shown) to the molding temperature that is somewhat lowerthan a melting point of the synthetic resin. The female mold 16 and thebottom bush 17 of the thermo-molding apparatus B are also heated andmaintained to a predetermined temperature level (usually about 80 toabout 150° C., about 50 to about 180° C. depending on the material ofthe sheet) by the heater 29. In this case, the temperature of the femalemold 16 and the bottom bush 17 should be controlled not to cool theheated sheet.

[0048] If the resin sheet S is made of PP and has a thickness of 1.0 mm,it is heated to about 140 to 200° C.

[0049] The upper mold C is lowered, and the lower mold is raised fromthe state of FIG. 2. As shown in FIG. 3, the heated sheet becomespinched and pressed between the clamp 11 of the upper mold C and the topsurface of the female mold 16 of the lower mold D. The plug 10 isfurther lowered relative to the clamp 11, the sheet S is forced toextend downwardly by the lower surface 13 of the plug 10, because thesheet is already heated and softened. At this time, since air is drawnthrough the gap 21 and the suction holes 25, the sheet S is drawn by thesuction holes 25, and comes to be held in tight contact with the innersurface of female mold above the suction holes 25. At this time,compressed fluid may be blown into the clamp 11 from above.

[0050] When the plug 10 is further lowered, the sheet S comes to be heldin tight contact with the mold surfaces 18, 19, 20 of the female mold 16and the top surface 26 of the bottom bush 17, as illustrated in FIG. 4.Thus, the sheet S is molded by the mold surfaces 18, 19, 20 and the topsurface 26, to produce the body wall 2, the bottom peripheral wall 5 andthe outer wall 7 a of the foot 4 of the container A.

[0051] As shown in FIGS. 4A and 4B, the plug 10 is stopped before itcontacts with the mold surface 19. As a result, a gap is formed betweenthe sheet S on the mold surface 19 and the lower surface 13 of the plug10. Air is drawn out through the gap when compressed air is blown intothe female mold 16 in a subsequent step as will be describedhereinafter. In the case of the illustrated embodiment, the gap is about0.1 to 0.5 mm.

[0052] By the above described vacuum sucking, resin “a” is drawn intothe gap 21 to produce the bulge 8 of the container. Since the resin “a”is drawn into the gap 21, the gap 21 is filled with the resin, so thateventually no resin is further drawn into the gap 21 any more. Thebottom bush 17 is heated to the above described predeterminedtemperature level by the heater 29, and the part of the sheet S thatcontacts with the top surface 26 of the bottom bush 17 is held to themolding temperature that is close to the melting point.

[0053] As described above, the sheet S is pressed and held in contactwith the mold surface 19 as a result of the air suction through thesuction holes 25 for producing vacuum (and due to the compressed air inthe clamp 11, if desired), the resin “a” of the lower end of the sheet Sis drawn into the gap 21, and the part of the sheet S that is held incontact with the top surface 26 is held to the molding temperature thatis close to the melting point. Under these circumstances, whencompressed fluid is blown into the female mold 16 through the blow-inholes 27, the part of the sheet S with the temperature level close tothe melting point is folded back along the lower edge of the outer wall7 a, and is moved upwardly, as illustrated in FIG. 5. Thus, the centralportion of the part of the sheet S with the temperature level close tothe melting point is brought into tight contact with the bottom surface13 of the plug 10, while the peripheral portion is folded back along thelower edge of the outer wall 7 a, and drawn to come into tight contactwith and fusion-bonded to the outer wall 7 a. In this way, the foot 4 isformed by fusion-bonding the outer wall 7 a and the inner wall 7 b asintegral parts thereof. FIG. 6 schematically illustrates a state wherethe operation of producing the footed and bottomed cylindrical containerby molding is completed.

[0054] At this time, since the peripheral part of the sheet S isexpanded, the peripheral section 6 b of the molded bottom wall 3 shows athickness smaller than the central section 6 a. Besides, since thetemperature of the sheet is maintained to a level close to the meltingpoint, the folded portion is fusion-bonded to the portion of the sheet Sthat is held in tight contact with the mold surface 20.

[0055] The central section can be made thin by using a plug having anupwardly curved lower surface for the molding operation using compressedair.

[0056] The thus formed container A is then cooled, and removed from themold. Subsequently, the outwardly directed flange 1 is formed by cuttingin a desired profile, to complete the operation of producing the footedand bottomed cylindrical container A.

[0057] The inner wall 7 b and the outer wall 7 a of the foot 4 of theobtained container A are in a completely fusion-bonded. In other words,they are integrally formed without any gap. It is a thin wall containerwhose body wall 2 and the bottom wall 3 are about 0.2 mm thick.

[0058] The above described first embodiment can be modified as follows.

[0059] In the above described embodiment, the plug 10 is stopped beforeit contacts the mold surface 19 of the female mold 16, and a gap isformed between the sheet S on the mold surface 19 and the lower surface13 of the plug 10, to allow the air (between the sheet S on the bush 17and the lower surface 13) left there to be drawn out. Alternatively, theplug 10 may be replaced by a plug 10 having a vent arranged between thelower surface 13 and the cylindrical wall surface 12. In suchmodification, the lower surface 13 of the plug 10 presses the sheet Sagainst the mold surface 19 for forming the bottom peripheral wall.

[0060] When the compressed fluid is blown through the blow-in holes 27in this modified embodiment, air between the sheet S on the bottom bush17 and the bottom surface 13 can be removed by the above described vent.

[0061] Still alternatively, if the bottom surface 13 of the plug 10 isstopped further before the mold surface 19 of the female mold 16 toproduce a gap of 0.5 to 1.5 mm between itself and the sheet surfaceafter the vacuum forming, and if the compressed fluid is blown throughthe blow-in holes 27, the bottom wall 3 will project above the bottomperipheral wall 5 by pressure forming.

[0062] Now, the second embodiment of the container, the thermo-moldingapparatus and the thermo-molding method to be used for molding thecontainer will be described below.

[0063] This embodiment of the invention relates to a bottomedcylindrical container (cup-shaped container).

[0064] Referring to FIG. 7, A′ denotes the bottomed cylindricalcontainer that comprises a body wall 31 having an outwardly directedflange 30 arranged along a peripheral edge of the opening, and a bottomwall 32.

[0065] A lower end of the body wall 31 is a grounding edge 33 of thecontainer. The body wall 31 is inwardly folded back along the groundingedge 33 to produce an inner wall 34. A top edge 35 of the inner wall 34connects to the bottom wall 32.

[0066] The inner wall 34 is fusion-bonded or welded to an innerperiphery of the part of the body wall 31 located under the top edge 35,and no gap is found between the body wall 31 and the inner wall 34.

[0067] The method of thermo-molding the container according to thesecond embodiment of the invention will be described below.

[0068] The thermo-molding apparatus in the second embodiment is obtainedby modifying the lower mold of the first embodiment of the invention.Therefore, the components that are same as those of the first embodimentare denoted by the same reference numerals and affixed by “a”. Thedifferences of the second embodiment and the first embodiment will bedescribed specifically.

[0069] Referring to FIG. 8, reference symbol C′ denotes the upper mold,and D′ denotes the lower mold.

[0070] As in the case of the above described first embodiment, the uppermold C′ comprises a cylindrical clamp 11 a and a plug 10 a verticallymovable relative to the clamp 11 a. The sheet S′ is heated by a heater(not shown). The plug 10 a has a cylindrical wall surface 12 a and aflat bottom surface 13 a. While the clamp 11 a is so designed thatcompressed fluid (such as compressed air) is blown into it from above,it is not essential to blow compressed fluid into the clamp 11 a.

[0071] The lower mold D′ comprises a mold base 15 a, a female mold 16 aarranged on the mold base 15 a, and a bottom bush 17 a arranged in aninside of the mold base 15 a.

[0072] The female mold 16 a has a mold surface 40 for forming the bodywall 31 of the container A′ to be molded. A passage 21 a is arranged atthe lower peripheral edge of the mold surface 40, so that a gap 21 a isprovided between the lower surface of the female mold 16 a and the moldbase 15 a. The gap 21 a communicates with an annular suction groove 22a, which suction groove 22 a communicates with a vacuum device (notshown).

[0073] A number of blow-in holes 27 a are formed at a center of the topsurface 26 a of the bottom bush 17 a. The blow-in holes 27 a communicatewith a source of compressed fluid (not shown).

[0074] The bottom bush 17 a is provided with a heater 29 a.

[0075] Now, the method of thermo-molding the container according to thesecond embodiment of the invention will be described below.

[0076] For the purpose of thermo-molding, the sheet S′ is heated by aheater (not shown) to the molding temperature that is somewhat lowerthan the melting point of the synthetic resin. The female mold 16 a andthe bottom bush 17 a of the thermo-molding apparatus B′ are alsomaintained to the above described predetermined temperature level by theheater 29 a.

[0077] The heated sheet S′ is pinched and pressed between the clamp 11 aof the upper mold C′ and the top surface of the female mold 16 a of thelower mold D′. The plug 10 a is further lowered relative to the clamp 11a, the sheet S′ is forced to extend downwardly by the lower surface 13 aof the plug 10 a, because the sheet is already heated and softened. Atthis time, compressed air is blown from the above, and air is drawnthrough the gap 21 a on the lower surface of the female mold 16 a toproduce vacuum, so that the sheet S′ is drawn by the gap 21 a. As aresult, the sheet S′ comes to be held in tight contact with mold surface40 of female mold 16 a.

[0078] The plug 10 a is further lowered and stopped before it contactswith the mold surface 40 of the female mold 16 a, as shown in FIG. 8. Asa result, the sheet S′ is brought into tight contact with the moldsurface 40 of the female mold 16 a and the top surface 26 a of thebottom bush 17 a, and molded to show a profile defined by the moldsurface 40 of the female mold 16 a and the top surface 26 a of thebottom bush 17 a. At this time, the sheet produces portions that becomethe body wall 31 and the bottom wall 32 of the container A′.

[0079] As in the case of the above described first embodiment, resin ais drawn into the gap 21 a by the air drawing operation or the vacuumsucking. The bottom bush 17 a is heated to the above describedpredetermined temperature level by the heater 29 a. The part of thesheet that contacts with the top surface 26 a of the bottom bush 17 a isheld to the molding temperature that is close to the melting point.

[0080] In this way, by the vacuum sucking and the compressed fluid, thesheet S′ is pressed between the mold surface 40 and the top surface 26 aof the bottom bush 17 a, and the resin “a” of the lower end portion ofthe body wall 31 of the sheet S′ is drawn into the gap 21 a. Then, asshown in FIG. 9, compressed air is blown into through the blow-in holes27 a of the bottom bush 17 a. The portion of the sheet held on the topsurface 26 a is folded back along the grounding edge 33. In this case,the central portion of the sheet is brought into tight contact with thebottom surface 13 a of the plug 10 a, while the peripheral portion ofthe sheet is brought into tight contact with and fusion-bonded to theinner peripheral surface of the body wall 31. Thus, as shown in FIG. 7,a bottomed cylindrical container A′ whose inner wall 34 produced byfolding back along the grounding edge 33 of the body wall 31 isfusion-bonded to the body wall 31 is obtained.

[0081] The present invention provides the following advantages.

[0082] A footed and bottomed cylindrical container according to theinvention does not have any gap on the inner surface of the container ata site corresponding to the foot where food can enter.

[0083] In a bottomed cylindrical container according to the invention,the inner wall produced by folding back the body wall along thegrounding edge thereof is welded to the body wall and hence no gap wherefood can enter is produced there.

[0084] When a bottomed cylindrical container according to the inventionis filled with hot food, sealed and then cooled to reduce the innerpressure, the bottom wall of the container operates to absorb the impactof pressure reduction to prevent any deformation or recession of thesealed surface because the container has a thin the bottom wall, or atleast a then peripheral portion in the bottom wall.

[0085] Since a thermo-molding method and a thermo-molding apparatusaccording to the invention is adapted to mold a ring-shaped foot or abottom wall by using compressed air and welding the resin layer of theinner peripheral portion and that of the outer peripheral portion of thefoot for a bottomed cylindrical container, the foot is formed withoutgap if the thickness of the material resin sheet fluctuates. Similarly,since the inner wall produced by folding back the body wall along thegrounding edge thereof and welded to the body wall for a cup-shapedcontainer, no gap is formed between the body wall and the inner wall ifthe thickness of the material resin sheet fluctuates.

[0086] Therefore, containers showing a same profile can be produced byusing different material resin sheets that may have differentthicknesses by means of a same thermo-molding apparatus.

[0087] Thus, containers having a small wall thickness can be produced byusing a thin material resin sheet to save the material depending on theapplications of the containers.

[0088] Since the present invention imposes no restrictions on thethickness of the material resin sheet, a bottomed cylindrical containercan be produced simply by bringing the bottom surface of the plug of athermo-molding apparatus according to the invention into contact with orclose to the mold surface of the peripheral wall of the bottom of thefemale mold of the apparatus regardless of the size of container.

[0089] Small containers can be produced by using a thin material resinsheet.

1. A bottomed cylindrical container, comprising a body wall, a bottomwall, and a ring-shaped foot downwardly extending from the bottom wall,said container being produced by thermo-molding a resin sheet,characterized in that said foot is formed by folding an inner wall bycompressed fluid to be fusion-bonded with an outer wall, so as to formthe foot comprising the inner wall and the outer wall.
 2. The bottomedcylindrical container according to claim 1, wherein said bottom wallcomprises a central section and a peripheral section, and the peripheralportion is made thin.
 3. A bottomed cylindrical container, comprising abody wall having a grounding edge at a lower end thereof, and a bottomwall, said container being produced by thermo-molding a resin sheet,characterized in that said bottom wall connects with an upper edge of aninner wall produced by folding back the body wall along the groundingedge and by fusion-bonding it to an inner periphery of the body wall. 4.An apparatus for thermo-molding a resin sheet to a bottomed cylindricalcontainer, comprising an upper mold having a plug, and a lower moldhaving a female mold and a bottom bush, wherein said female mold hasmold surfaces for forming a body wall of the container, and said bottombush has compressed air blow-in holes.
 5. An apparatus forthermo-molding a resin sheet to a bottomed cylindrical container with aring-shaped foot, comprising an upper mold having a plug, and a lowermold having a female mold and a bottom bush, wherein said female mold isprovided with suction holes, said female mold has a mold surface forforming a body wall of the container, a mold surface for forming abottom peripheral wall of the container, and a mold surface for formingan outer wall of the foot, and said bottom bush has compressed fluidblow-in holes.
 6. The apparatus according to claim 4, wherein said lowermold comprises a mold base, the bottom bush in the mold base, and thefemale mold on the mold base, a gap is formed between a lower surface ofthe female mold and the mold base, and an annular suction groove isformed between a lower surface of the female mold and the mold base, andcommunicates with the gap.
 7. A method for thermo-molding a footed andbottomed cylindrical container, comprising heating a thermoplastic resinsheet, pressing the heated sheet by a plug of an upper mold withvacuum-sucking, to contact the sheet with mold surfaces of a female moldof a lower mold, so as to form a body wall and an outer wall of a footof the container, and blowing compressed fluid through blow-in holes ofa bottom bush of the lower mold into the female mold withvacuum-sucking, to contact the sheet on a top surface of the bottom bushwith a bottom surface of the plug, so as to form a bottom wall and aninner wall of the foot, said inner wall being fusion-bonded with theouter wall.
 8. A method for thermo-molding a bottomed cylindricalcontainer, comprising: heating a thermoplastic resin sheet, pressing theheated sheet by a plug of an upper mold with vacuum-sucking, to contactthe sheet with mold surfaces of a femal mold of a lower mold, so as toform a body wall of the container, and blowing compressed fluid throughblow-in holes of a bottom bush of the lower mold into the female moldwith vacuum-sucking, to contact the sheet on a top surface of the bottombush with a bottom surface of the plug, so as to form a bottom wall andan inner wall being fusion-bonded with the body wall.
 9. The apparatusaccording to claim 5, wherein said lower mold comprises a mold base, thebottom bush in the mold base, and the female mold on the mold base, agap is formed between a lower surface of the female mold and the moldbase, and an annular suction groove is formed between a lower surface ofthe female mold and the mold base, and communicates with the gap.